Device for stimulating living tissue

ABSTRACT

A device for stimulating heart tissue contains a stimulation unit connected via a switching device to an electrode system. The number of connecting lines between the stimulation unit and the switching device is minimized by emitting control signals and stimulation pulses from a common pulse signal output socket of the stimulation unit. The switching device contains a signal discriminator which separates the control signals from the stimulation pulses, the control signals then controlling the switching device such that the stimulation pulses are delivered to a specific part of the electrode system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for stimulating living tissue,of the type having a stimulation unit which emits stimulation pulsesfrom a pulse signal output socket, an electrode system which deliversthe stimulation pulses to the living tissue, a controllable switchingdevice connected between the electrode system and the pulse signaloutput socket for transmitting the stimulation pulses to a specific partof the electrode system, and a control device which emits controlsignals from a control output socket to a control input socket on theswitching device to control the transmission of stimulation pulses.

2. Description of the Prior Art

A device of the type generally described above is disclosed in U.S. Pat.No. 4,628,934. This known device contains a pacemaker, a switching unitand an electrode system. The electrode system consists of two multipolarelectrodes which can be unipolarly or bipolarly connected to thepacemaker via the switching unit. The switching unit is controllable,and is directly controlled from pacemaker electronic circuitry viacontrol lines.

By means of the switching unit, the required number of feedthroughs topacemaker electronic circuitry, which is enclosed in a pacemaker case,can be reduced. In a unipolar version, one feedthrough is employed fordelivering stimulation pulses from pacemaker electronic circuitry andcontrol lines for controlling the switching unit. In a bipolar version,there are two feedthroughs, each with a line for delivering stimulationpulses, and control lines to the switching unit. In one version of thisknown device, a serial-to-parallel signal converter is employed in theswitching unit to reduce to one the number of control lines to thepacemaker electronic circuitry. A pulse train, which in theserial-to-parallel signal converter is applied in parallel to theswitches in the switching unit, is then fed through this single controlline. When the switching device is devised in the form of a detachableadapter for a pacemaker, two electrodes can be coupled, via the adapter,to a pacemaker designed for one electrode.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a device of the typegenerally described above in which the number of feedthroughs is furtherreduced.

It is a further object of the to provide such a device which can easilybe adapted to a plurality of functions in, e.g., the diagnosis ortherapeutic treatment of living tissue.

Such a device is achieved in accordance with the principles of thepresent invention having a control device with a control output socketwhich is coupled to the pulse signal output socket, switching devicewith a control input socket coupled to the pulse signal output socket,and wherein the switching device contains a signal discriminator toseparate control signals from stimulation pulses so that the controlsignals control the transmission of the stimulation pulses to thetissue.

The number of feedthroughs is thereby minimized. For a unipolar device,one feedthrough is sufficient through which stimulation pulses andcontrol signals are transmitted to the switching device and on to theelectrode system. In the corresponding way, a bipolar device has twofeedthroughs. The signal discriminator discriminates the different typesof signals and separates them so the control signal can be used forcontrolling the setting of the switching device. In a version of theinvention with a pacemaker, a plurality of electrodes can be placed in aheart and connected to the pacemaker via the switching device. Theheart's response to stimulation pulses at different locations in theheart can be easily studied so as to, e.g., ascertain the best site fora permanently implanted electrode.

One way of discriminating stimulation pulses and control signals isachieved in accordance with the invention in an embodiment wherein thecontrol signals and the stimulation pulses have different polarities,and the signal discriminator senses polarity in order to distinguishcontrol signals from stimulation pulses.

The different polarities make it easy to distinguish between the typesof signal. Regardless of whether the same or different polarities areused for the signals, it is advantageous for the control signals to havean amplitude lower than the threshold value required to stimulate theliving tissue, since there would then be no risk of erroneous tissuestimulation caused by control signals misdirected to the electrodesystem.

Alternatively, the signals can be discriminated in an embodiment whereinthe control device contains a modulator to modulate the stimulationpulses with the control signals, and the signal discriminator contains ademodulator to separate the control signals from the stimulation pulses.

In another embodiment of a device in accordance with the invention, atleast one measurement device is coupled, via the switching device, tothe pulse signal output socket, and the control device, by means of acontrol signal, closes a signal connection between the measurementdevice and a measurement appliance in the stimulation unit.

As a result, the device can be expanded into a multifunctional unitcapable of stimulating tissue and measuring physiological variables instimulated or other tissue. The measured variables can be used by thestimulation unit for enhanced monitoring and control of tissuestimulation. Physiological variables which can be measured are, e.g.,temperature, blood oxygen, tissue impedance and movements. When thecontrol signal closes the connection between the stimulation unit andthe measurement device, the measurement signal is sent from themeasurement device to the measurement appliance.

In this context, it is advantageous for the measurement device to becontrollable, for which purpose the control device emits measurementcontrol signals and the signal discriminator distinguishes betweencontrol signals for directing the stimulation pulses and measurementcontrol signals. The measurement control signals control thetransmission by the switching device of measurement control signals tothe measurement device.

The stimulation unit then provides complete control over all functionalunits in the device. The control signals open different connectionsbetween the stimulation unit and the electrode system or the measurementdevice over the switching device. The stimulation unit can control themeasurement device's measurement of the physiological variable, and alsoreceives the measurement signals from the measurement device, in orderto vary stimulation of the living tissue on the basis thereof.

In another embodiment of the device in accordance with the invention,the switching device contains a power supply input socket connected tothe pulse signal output socket, and the stimulation unit contains apower source which delivers power to the power supply input socket.

In this way, the power requirements of the switching device arecompletely fulfilled by the stimulation unit. Power can be transmittedas a supply current to the power supply input socket in the switchingdevice, or the switching device can contain a capacitor connected to thepower supply input socket through, and the power source charges thecapacitor.

One advantage in this context is that the power source is connected tothe measurement device through the switching device, and the powersource supplies current for the measurement device's power requirementswhen the connection between the power source and the measurement deviceis closed.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a first embodiment of a deviceconstructed in accordance with the principles of the present invention.

FIG. 2 is a block diagram of the stimulation unit in the device of FIG.1.

FIG. 3 is a block diagram of the switching device in the device of FIG.1.

FIGS. 4-6 respectively illustrate three different ways of sending acontrol signal and a stimulation pulse from the stimulation unit to theswitching device in the device of FIG. 1.

FIG. 7 is a schematic illustration of a second embodiment of a deviceconstructed in accordance with the principles of the present invention.

FIG. 8 is a block diagram of the stimulation unit in the device of FIG.7.

FIG. 9 is a block diagram of the switching device in the device of FIG.7.

FIGS. 10-11 respectively illustrate two different ways of sending aplurality of different signals from the stimulation unit to theswitching device in the device of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The device 1 in FIG. 1 has a stimulation unit in the form of a pacemaker2 which is connected, through a socket 3 and a switching device 4, to aheart 5 by an electrode system 6. The stimulation unit 2 could be adefibrillator or a cardioverter (or a combination of such devices), butfor simplicity will only be described henceforth as a pacemaker 2. Theelectrode system 6 consists of a first tip electrode 7 and a second tipelectrode 8 placed in the atrium of the heart 5, a third tip electrode 9and a fourth tip electrode 10 placed in the ventricle of the heart 5.The pacemaker 2 is unipolarly coupled and has an indifferent electrode11 on the exterior of the pacemaker 2 to conduct stimulation pulses backto the pacemaker from the electrode system 6. A stimulation pulse isgenerated by the pacemaker 2 and sent, along with a control signal, tothe switching device 4. The control signal changes the state of theswitching device 4 in such a way that the stimulation pulse is sent toone of the tip electrodes 7-10 in the electrode system 6 and deliveredto the heart 5. The stimulation pulse is then conducted over body tissueback to the indifferent electrode 11 and the pacemaker 2.

FIG. 2 shows a block diagram of the pacemaker 2, containing a pulsegenerator 12 connected to the pulse signal output socket 3 and theindifferent electrode 11, and a measurement appliance 13 which is alsoconnected to the pulse signal output socket 3 and the indifferentelectrode 11. The pulse generator 12 generates the stimulation pulses.The measurement appliance 13 senses the heart's electrical activityafter the switching device 4 closes a connection between the pacemaker 2and the electrode system 6. A control unit 14 controls the pulsegenerator 12 and the measurement appliance 13 via a data bus 15.Stimulation pulses can be modulated with control signals in a modulator16. The modulator 16 is also connected to the control unit 14 via thedata bus 15. Using a telemetry unit 17 and an extracorporeal programmingunit 18, a physician can program the control unit 14 to perform variousfunctions. The telemetry unit 17 is also connected to the data bus 15.Power for the pacemaker 2 is supplied by a battery 19.

Stimulation pulses with superimposed control signals are sent by thepulse generator 12 from the pulse signal output socket 3 to theswitching device 4. In the switching device 4, as shown in FIG. 3, thesignals in the switching device 4 are sent via a signal input socket 20to a signal discriminator 21 which demodulates the control signal andfeeds it to a control element 22 for controlling a switch 23. The switch23 has four output positions 23A-D respectively connected to the firsttip electrode 7, the second tip electrode 8, the third tip electrode 9and the fourth tip electrode 10. A line 24 connects the switch 23 to thesignal input socket 20 to transmit stimulation pulses across the switch23 to the selected electrode tip. The switching device 4 also contains adiode 25 and a capacitor connected in parallel with the line 24 to drivethe switching device 4. The diode 25 is connected to the signal inputsocket 20 and to the capacitor 26 which is connected across the powersupply input socket 27 of the switching device 4. An energy pulse,having a polarity opposite to the polarity of the stimulation pulses, isemitted to charge the capacitor 26 with the energy required to drive theswitching device 4.

Referring to FIGS. 4-6, three examples of stimulation pulses which canbe used in the device according to FIGS. 1-3 will be described below.FIG. 4 shows a first stimulation pulse 28 with a superimposed controlsignal 29. The stimulation pulse 28 is generated by the pulse generator12 with an amplitude and duration controlled by the control unit 14. Themodulator 16 modulates the control signal 29 over the first part of thestimulation pulse 28. The stimulation pulse 28 is sent from the pulsesignal output socket 3 to the signal input socket 20 of the switchingdevice 4. The control signal is demodulated in the signal discriminatorand fed to the control element 22 which sends a switching signal to theswitch 23. For example, if the pacemaker is to deliver a stimulationpulse to the atrium of the heart 5 via the first tip electrode 7, thecontrol signal indicates that the switch 23 must enable output position23A which is connected to the first tip electrode 7. The stimulationpulse 28 is thereby transmitted from the signal input socket 20 via line24 to the switch 23 and through output position 23A to the first tipelectrode 7, which delivers the stimulation pulse 28 to the heart 5. Thestimulation pulse 28 is then conducted through body tissue back to theindifferent electrode 11 and the pulse generator 12.

FIG. 5 shows a second stimulation pulse 30 which contains a firstcontrol signal in the form of a pulse packet 31, a first stimulationpulse part 32, a second control signal in the form of a pulse packet 33and a second stimulation pulse part 34. The first control signal 31 can,e.g., cause transmission of the first stimulation pulse part 31 to theheart 5 via the third tip electrode 9, and the second control signal 33can set the switch 23 such that the second stimulation pulse part 34 isdelivered to the heart 5 via the fourth tip electrode 10.

FIG. 6 shows a third stimulation pulse 35 in which the control signal 36consists of a high-frequency signal 30, superimposed on the stimulationpulse 35.

A second embodiment of the device according to the invention is shown inFIG. 7. The device 37 includes a pacemaker 38 for bipolar operationwhich is connected, via a pulse signal output socket 39 and a switchingdevice 40, to a first measurement device 41, a second measurement device42 and, through an electrode system 44, to a heart 43. For unipolaroperation, the pacemaker 38 has an indifferent electrode 49 on its case.The electrode system 44 includes a first tip electrode 45 and a firstring electrode 46 placed in the atrium of the heart 43, and a second tipelectrode 47 and a second ring electrode 48 placed in the ventricle ofthe heart 43. A stimulation pulse generated by the pacemaker 38 and acontrol signal are simultaneously emitted and act on the switch 40 tocomplete a connection with, e.g., the second tip electrode 47, whichdelivers the stimulation pulse to the heart 43, and the second ringelectrode 48, via which the stimulation pulse is conducted back to thepacemaker 38.

As FIG. 8 shows, the pacemaker 38 contains, like the pacemaker 2 in FIG.2, a pulse generator 50, a measurement appliance 51 (such as a signalevaluation unit, which may also transmit signals to the measurementdevices 41 and 42), a control unit 52 and a telemetry unit 53, allconnected to each other via a data bus 54. The telemetry unit 53transmits programming and information data between the control device 52and an extracorporeal programming unit 55. The pacemaker 38 alsocontains a control signal generator 56 and a power source 57, bothconnected to the pulse signal output socket 39. The pulse generator 50,the control-signal generator 56 and the power source 57 are shown asthree separate units for clarity, but could consist of a single unit.All pacemaker electronic circuitry is supplied with power by the battery58. With the control signal generator 56, the control device 52 controlsthe switching device 40 to connect the first measurement device 41 orthe second measurement device 42 or any of the electrodes 45, 46, 47, 48of the electrode system 44 to the pulse signal output socket 39.

As shown in FIG. 9, the switching device 40 has a signal input socket 59which is connected to the pulse signal output socket 39 and whichconducts signals from the pulse signal output socket 39 to a signaldiscriminator 60 to separate the control signal and send it to a controlelement 61. The control element 61 controls a first switch 62 and asecond switch 63. The first switch 61 has five output positions 62A-E,the first output position 62A connected to the first measurement device41, the second output position 62B connected to the second measurementdevice 42, the third output position 62C connected to the first tipelectrode 45 and the fourth output position 62D connected to the secondtip electrode 47. The fifth output position 62E has no furtherconnection. The second switch 63 has three output positions 63A-C, thefirst output position 63A connected to the first ring electrode 46, thesecond output position 63B connected to the second ring electrode 48,the third output position 63C having no further connection. A first line64 connects the signal input socket 59 to the first switch 62, and asecond line 65 connects the signal input socket 59 to the second switch63.

A series-connected diode 66 and capacitor 67 are connected in parallelacross the signal input socket 59, the capacitor 67 being charged fromthe pacemaker 38 in order to supply the switching device 40 with powerthrough a power supply input socket 68.

Referring to FIGS. 10 and 11, two examples of signal transmission whichcan be used in the device 37 according to FIG. 7-9 will be describedbelow. FIG. 10 shows an energy pulse 70, generated by the power source57, to charge the capacitor 67. The switching device 40 is in its outputmode, i.e., the first switch 62 is in its fifth position 62E and thesecond switch 63 is in its third position 63C. A control signal 69follows the energy pulse 70 and causes the first switch 62 to be set atits third position 62C in order to send the stimulation pulse 71 to thefirst tip electrode 45, and sets the second switch 63 to its firstposition 63A so as to conduct the stimulation pulse 71 back to the pulsegenerator 50 over the first ring electrode 46 and the switching device40. The stimulation pulse 71 can also be emitted unipolarly, whereby thesecond switch 63 is set at its third output position 63C, and theconnection between the indifferent electrode 49 and the pulse generator50 is closed.

FIG. 11 shows a first energy pulse 73a for charging the capacitor 67. Afirst control signal 72a closes the connection between the measurementappliance 51 and the first measurement device 41, a measurement signal74a then being transmitted from the first measurement device 41 to themeasurement appliance 51. A second control signal 72b sets the switch 62such that the connection to the second control device 42 is closed. Themeasurement appliance 57 emits a second energy pulse 73b followed by ameasurement control signal 74b generated by the power source 57 in orderto supply the second measurement device 42 with power and to controlsame. The second measurement device 42 may have a capacitor which ischarged by the second energy pulse 73b. A third control signal 72dcauses the connection with the second tip electrode 47 and the secondring electrode 48 to close so a stimulation pulse 75 is delivered to theheart 43.

The switches 23, 62, 63 in FIGS. 3 and 9 can be devised with, e.g.,transistors or in some other known manner. Power for the switchingdevice 40 can also be provided in some way other than with a capacitor67 which is charged, viz. by having the power source 57 emit a supplycurrent sufficient for the power requirements of the switching device40.

Although modifications and changes may be suggested by those skilled inthe art, it is the intention of the inventors to embody within thepatent warranted hereon all changes and modifications as reasonably andproperly come within the scope of their contribution to the art.

We claim as our invention:
 1. A device for stimulating living tissue comprising:stimulation pulse generator means, having an output socket, for generating a stimulation signal having a polarity at said output socket; electrode means having a plurality of stimulation signal delivery elements for transmitting said stimulation signal to different tissue sites; control means, having a control means output connected to said output socket, for generating a control signal at said control means output, said control signal having a polarity opposite to the polarity of said stimulation signal and being superimposed on said stimulation signal at said output socket; switching means, responsive to said control signal and having an input connected to said output socket which receives said stimulation signal with said control signal superimposed thereon and having outputs connected to said electrode means, for directing said stimulation signal to a selected tissue site, determined by said control signal, via at least one of said delivery elements; and discriminator means in said switching means for separating said control signal from said stimulation signal before directing said stimulation signal to said selected tissue site.
 2. A device as claimed in claim 1 wherein said control means comprises means for generating said control signal with an amplitude lower than an amplitude capable of stimulating said living tissue.
 3. A device as claimed in claim I wherein said control means comprises means for modulating said stimulation signal with said control signal to form a modulated signal and wherein said discriminator means comprises means for demodulating said modulated signal to separate said stimulation signal and said control signal.
 4. A device as claimed in claim I wherein said switching means has a power supply input connected to said output socket, and wherein said stimulation pulse generator means includes a power source connected to said output socket for supplying power to said power supply input.
 5. A device as claimed in claim 4 wherein said switching means draws a supply current, and wherein said power source supplies said supply current to said switching device through said output socket.
 6. A device as claimed in claim 4 wherein said switching means includes a capacitor connected to said power supply input and to said electrode means, said power source charging said capacitor. 